Hi all my collection of Bonsai plants have green moss growing and covering the tops of the pots.Some of the moss is starting to grow up the trunks of the plants.Is this going to cause any problems?I planted the moss on the pots because I liked the look, its growing very well.

Yes Dolicus, it sure can cause problems. Because moss is always damp, it keeps the bark under it damp as well and this can cause the bark - and then the inner layers to rot away. Very few trees can stand having their trunks permanently wet - Swamp Cypress is one exception, and they can also tolerate moss growing up the trunk with no ill-effects.

Think of it this way: If you kept the small Casuarina you have in your garden sitting permanently in water just above the base, the trunk would rot away. I guess that's why we're always told that when planting something in the garden, to always plant at the original soil level otherwise you run the risk of collar rot. It's the same with Bonsai - figs will rot fairly quickly if they have moss on the base of the trunk. The root structure of most plants and trees are designed to be permanently moist. Exposing some roots to the air by lifting a Bonsai in its pot doesn't cause any problems, but lowering it can. Another problem about having moss on your trees is that the moss sends out very fine 'filigree' roots that penetrate the outer layers of the bark, allowing moisture and possibly other nasties to get behind it.

There's nothing wrong with having moss on your pots, but keep it a couple of centimetres away from the trunk and any roots that have been exposed to the air and converted to proper bark.

I would seriously consider removing the moss from the trunks, wait a few days to allow the bark to dry out again and then use a small nail or toothbrush and some soapy water to scrub any residue away. Don't be too heavy handed with the scrubbing though - you don't want to damage the bark.

Another thing to consider is if the moss is left to get really thick, it can stop water getting through to the soil mix and although water might run out the drain holes, it's because the water has gone down the inner sides of the pot and not through the moss. I know this to be true, because many years ago I had a tree that I was 'nurturing' moss to grow on top of the soil. I had a lovely lush growth going but the tree started to look sickly with yellowing leaves and leaves falling off. I thought "This is weird - the moss is very lush and dark green but the tree doesn't look too good at all". I asked someone who knew a lot more about Bonsai than I did at that time, and as soon as he saw it, he told me to take the moss off and re-pot the tree - the soil had dried out and become water repellent because the moss was starving it of water. The moss was getting watered, but the rest was just running off. He also told me that most people only put moss on a few days to a week or so before they intend displaying them. If you keep that gap I suggested between the trunk and the moss, that will ensure an adequate supply of water can get through to where it's needed and you can leave the rest of the moss in place if you want to. Bonsai do look good with moss on the pots - they look as if they are in a more natural setting.

I only put moss on my pots when I'm displaying my trees. Once I get them home again, the moss gets taken off and re-laid in my shade-house. I've got two beds of it growing. One is about a metre square, the other about 1/2 metre square.

No matter, just put it down to a learning curve - bet you won't do it again .

Try doing what I suggested about cleaning it off and let the damaged areas dry out. Over time and with an increase in growth, the damaged areas may callous over, but it's doubtful in the small pots. The trees would need to be re-potted into large black plastics or styrene boxes.

To stop them rotting any further, when they've dried out thoroughly, you could paint them with Lime/Sulphur solution, but make sure they really have dried out - even scrape some of the mix away to expose more of the lower trunk. Another product you could use is wood hardener available from Bunnings or other good hardware stores. Be careful though, they really do need to be totally dry in the affected areas before using either.

Something else you could do to save them is to take them out of those pots, cut 'windows' in the bark around the trunk just above the damaged areas, treat the windows with hormone rooting gel or powder and plant them deeper in black plastics above the windows. Effectively, what this is, is a ground layer and is not as invasive as an aerial layer.

I'm just about to do a post where I've stuffed up a bit on a fig, so you're not alone Dolicus